how do you find a sites upline.....or who is hosting them ???

Do you mean like upstream provider? Use tools like www.network-tools.com and www.arin.net to determine where a source IP is being hosted and who their upstream is. Simple trace routes can determine this as well.

To detect how many websites a host has there are known DNS tools to do this but I've found them very unreliable. Maybe ask the host but most of the time the list will be nothing or small because most hosts have a privacy policy which protects their client’s information (including URLs) from being released.

you could do a traceroute.

assuming you're on a windows box...

open up the command window (c prompt)
type in tracert domain.com or tracert <ip> and it should display the path it takes to reach a website.

Check out http://www.visualware.com/visualroute/index.html for a visual depiction of what happens..